Published German patent application No. 2,426,343 describes an apparatus in which the rotary anode radio-generator tube supplies a wide beam of small thickness in the form of a sector or a fan, for the simultaneous irradiation through a complete section of the body which is to be examined, of several measuring detectors which are aligned and placed side by side. In this apparatus, several reference detectors of little bulk such as semiconductor diodes, are situated at the level of the inlet of the collimator which renders it possible to define the sector-shaped beam. The signals from these detectors are combined in a calculator circuit in order to determine the intensity of the radiation provided by the tube at each point of the beam and to compensate the overall and localised variations in the region of each measuring detector.
A second prior art device is that of published French Pat. No. 2,235,854 which describes an axial tomography apparatus comprising a reference detector intended to measure the intensity of the radiation supplied by an X-ray tube, a beam which irradiates the body which is to be examined, and through the latter, a measuring detector intended to measure the intensity of the radiation downstream of the body or member which is to be examined, the ratio between the signals delivered respectively by the measuring detectors and the reference detectors corresponding to the absorption of the radiation by this body. This reference detector comprises a scintillator af low absorption as regards X-rays, of which the absorption of the X-rays passing through the same is lower than 10 per 100, of which the absorption of the visible light emitted by itself is negligible, and which is arranged in such manner as to intercept the beam as a whole. The beam reaching the reference detector encompasses the whole of the useful beam reaching the measuring detector and is centred on this beam, the surface of the reference detector irradiated by the reference beam being at least equal to that of the measuring detector illuminated by the useful beam. The aperture of the beam reaching the reference detector is selected to be, for example, 10 to 20 times greater than that of the useful beam so as to obtain at the output side of this reference detector, a reference signal which has a level comparable to that of the measuring detector and of which the intensity variations due to the alternate heating and to its instability, to the rotation and faults of the surface of the anode as well as to the vibrations of this latter, are sufficiently close to those of the useful beam to compensate these in a very satisfactory manner, which is not so in the case of the devices which utilise as a reference an X-ray beam which does not encompass the whole of the useful beam as in the aforesaid prior art (point detectors), since the radiation diagram may equally vary with the rotation.
The first document mentioned makes it possible to compensate for an intensity variation as a function of the direction of the sector-like beam of the measuring detector in question.
The second document mentioned makes it possible to take into consideration the whole of the useful beam.
These devices make it possible to compensate for a variation of the quality of the beam related, for example, to the high voltage applied to the X-ray tube, but do not allow for the fact that the objects which are to be analysed are not uniform. The reference detector device of the invention makes it possible to mitigate this disadvantage by associating with the reference detectors compensating filters reproducing the most current objects from the point of view of X-ray attenuation.